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Firstly, it appears that you aren't closing the first <a> tag.
I would guess that this is creating the problem as the browser is attempting to start the second link definition before it has been told where first link defination ends causing a problematic overlap in the structure of the javascript instructions ('syntax error').

This should provide an error-free, 'belts and braces' link that will create a popup if javascript it enabled, but will simply forward the existing browser window to the destination url if javascript isn't enabled.

Also, it would be better for your markup if you were to wrap the guts of the popup code into a header/externalised function.
The destination url could remain as a variable which means you'd only need to call the function and mention the url, rather than repeat the entire window.open(…) procedure again.

e.g.

in the head of your current page (or in an 'external js file' linked to in the header of your current page*):

1. The two bits of code should be used together.
The first part (head/external) simply predefines what the function should do when it's called.
The second part (body) shows how the link tag <a> should be structured so as to call the prescribed function and also how to tell the function which url (variable) to use in the popup window.

2. this.href is kinda like javascript shorthand for saying that 'the href that is also present in this <a> tag.

You could alternatively rewrite the entire destination url in place of this.href and it would work exactly the same.
I choose to use this.href i these cases as it saves on repeating code.

By using the destination url in the href value and referring back to it in the javascript function with this.href, you only need to change the (long) url in one place rather than two, when making changes.